2-Ethylhexanoic acid has caused eye damage in one individual, eye irritation in rabbits and skin irritation in rats and rabbits. It was of low to moderate toxicity in acute studies by the oral, dermal and inhalation routes in laboratory animals. On repeated oral administration to rodents it induced tissue changes in the liver, stomach and kidneys and in particular caused proliferation of liver peroxisomes (cellular substructures) together with an increased activity of certain liver enzymes. 2-Ethylhexanoic acid caused foetal malformations and foetal deaths in rats treated orally during pregnancy. It was not mutagenic in an Ames bacterial test.